Fuel for nuclear power plants is produced by uranium enrichment processes requiring uranium hexafluoride (UF6) as a feed or input. UF6 is commonly produced by the fluorination of uranium tetrafluoride (UF4), which is, in turn, commonly produced utilizing a multi-stage hydrofluorination process. During a typical multi-stage hydrofluorination process, uranium dioxide (UO2) is introduced as a solid feed into a first fluidized bed hydrofluorination reactor (referred to herein as the “primary hydrofluorinator”) and contacted with partially-reacted hydrogen fluoride (HF) gas to produce partially-reacted UF4. The partially-reacted UF4 is then supplied to a second fluidized bed hydrofluorination reactor (referred to herein as the “secondary hydrofluorinator”) within which the UF4 is contacted with a fresh HF gas feed. This second stage hydrofluorination process results in the production of fully-reacted UF4, which is then withdrawn from the secondary hydrofluorinator through a lower solids outlet. The partially-reacted gas produced pursuant to the second stage hydrofluorination reaction is withdrawn from the secondary hydrofluorinator through an upper manifold and recycled back to a single-chamber plenum disposed beneath the reaction chamber of the primary hydrofluorinator. The partially-reacted gas is supplied to the plenum via a gas/solids inlet pipe, which penetrates through the plenum's annular sidewall along an axis projecting through the plenum's center. The partially-reacted gas reorients within the plenum before flowing into a gas distributor (e.g., a perforated plate or sintered grate), which injects the gas into the primary hydrofluorinator's reaction chamber for further reaction with newly-supplied UO2.
Particulate solids inevitably become entrained in the partially-reacted gas withdrawn from the secondary hydrofluorinator and supplied to the single-chamber plenum of the primary hydrofluorinator. The larger entrained particles, which may have diameters approaching those of the gas flow openings provided in the gas distributor, can potentially clog the distributor's gas flow openings as an aggregate mass. Clogging of the distributor's gas flow openings not only impedes gas flow through the distributor, but also results in the maldistrubtion of hydrogen fluoride gas within the primary reaction chamber. The maldistrubtion of HF gas reduces the overall efficacy of the hydrofluorination reaction and produces dead zones along the upper face of the gas distributor, which increase the likelihood of areas of extreme localized heating (commonly referred to as “hot spots”) developing within the reaction chamber. Gas distributor clogging may ultimately necessitate shutdown of the hydrofluorination unit to allow cleaning of the gas distributor, which adds undesired expense and delay to the hydrofluorination process. While one or more freestanding particulate filters may be disposed upstream of the primary hydrofluorinator to reduce the quantity of entrained solids reaching the gas distributor, such filters require routine maintenance to replace or clean of saturated filter elements and thus also necessitate periodic shutdown of the hydrofluorination unit.
It would thus be desirable to provide embodiments of a series-coupled fluidized bed reactor unit, such as a multi-stage fluidized bed hydrofluorination unit, wherein clogging of a gas distributor included within the unit is minimized or eliminated by removal of entrained solids from a partially-reacted gas stream supplied to the gas distributor. Ideally, embodiments of such a series-coupled fluidized bed reactor unit would enable the continual and uninterrupted removal of larger entrained solids from the partially-reacted gas stream with minimal maintenance requirements. It would also be desirable to provide embodiments of a hydrofluorination process carried-out utilizing such a series-coupled fluidized bed reactor unit. Other desirable features and characteristics of the present invention will become apparent from the subsequent Detailed Description and the appended Claims, taken in conjunction with the accompanying Drawings and the foregoing Background.